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BULLETIN CARNEGIE MUSEUM OF NATURAL HISTORY NO. 32
nent is present. The peripheral gular pattern is the
standard reticulate form.
Anterior and posterior collar markings are only
variably present with both sexes usually lacking pos-
terior collar markings and females often lacking both
the posterior and anterior collar components. When
present, the posterior collar markings are reduced
and do not approach one another middorsally. The
anterior collars are complete ventrally in adult males,
with black pigments extending through the gular
fold. A pair of black nuchal spots are not present
middorsally between the anterior collar markings.
Enlarged melanic axillary patches immediately pos-
terior to the forelimb insertion are variably present.
Large melanic inguinal patches are always present
in adult males. The femoral pores are generally off-
white to gray in color. Paired, melanic keels are
absent from the ventral surface of the caudal ex-
tremity.
Females are less vividly marked than males. The
head and gular markings are less vibrantly marked
and they lack male color pattern characteristics such
as the white dorsal caudal stripe and melanic in-
guinal patches, axillary patches, central gular patch,
and ventrally complete anterior collar marking. Fe-
males develop vivid orange or reddish lateral bars
during the gravid period. The tail is not vividly
colored in adult or subadult females of this species.
Size. -This species exhibits strong sexual dimor-
phism with males reaching larger adult size (maxi-
mum observed SVL = 120 mm) than females (max-
imum observed SVL = 104 mm).
Distribution (Fig. 48).-Restricted to Isla Angel
de La Guarda in the Gulf of California, Mexico.
Fossil Record. -None.
Natural his tor)^. -No published accounts are
available regarding the natural history of Crotaphy-
ttcs insularis. However, this species does not appear
to differ markedly with respect to its behavior and
ecology from its sister taxon, C. vestigiunt. Adults
were observed basking on isolated volcanic rocks
and a juvenile was basking on a talus slope com-
prised of smaller white stones. Individuals are wide-
ly spaced, which may be the result ofextremely xeric
conditions with very scant vegetation. Adults ofboth
sexes and juveniles were active on 28 and 29 June
199 1 and one female was observed with gravid col-
oration.
Illustrations. -A color photograph was provided
by Sprackland (1 993).
Crotaphytus nebrius
Axtell and Montanucci, new combination
(Fig. 3 1 A)
Croraphj~ius collaris nebriw Axtell and Montanucci. 1977: 1; fig.
1. Type locality: "28°30'30'N-111002'30*W" (14 Km bv road
N. Rancho cienepuita), Sonora, Mexico" (hilotype: ~ ACM
1266 17).
Er)arrology.-From the Greek nebrias, meaning spotted, like
a fawn. Named in reference to the fawn-like dorsal pattern of
large white spots on a pale tan field.
Diagnosis. - Crotaphy us nebrius can be distin-
guished from C. dickersonae, C. grismeri. C. bi-
cinctures, C. vestigium, and C. insularis by the ab-
sence in adult males of a laterally compressed tail,
enlarged dark brown or black inguinal patches that
extend between one-third and one-half the distance
between the hindlimb and forelimb insertions, and
a pale white dorsal caudal stripe. It can be funher
distinguished from C. grismeri, C. bicinctores, C.
vestigium, and C. insularis by the presence of black
oral melanin. It can be distinguished from C. reti-
cufatus and C. antiquits by its dorsal color pattern
of white spots on a pale tan field, rather than white
reticulations on a pale tan or brown field and the
absence of jet black femoral pores in males. It can
be further distinguished from C. reticulatus by the
presence in adult males of small dark brown or black
inguinal patches. It can be distinguished from C.
collaris by the presence in adult males ofdark brown
or black pigmentation in the gular fold (= ventrally
complete anterior collar) and by the presence of burnt
orange ventrolateral abdominal coloration in breed-
ing males.
Ifariation (n = 20). - Rostral approximately four
times wider than high, usually rectangular in shape.
Rostral bordered by three to six postrostrals. Re-
maining snout scales irregularly arranged, an en-
larged middorsal series may be present. Nasals sep-
arated by four to six internasals. Frontonasals oc-
casionally enlarged. Canthals three; five to eight
scales separate canthals of left and right sides. Su-
praorbital semicircles present with ten to 15 scales
per semicircle, median scales do not fuse to form
azygous frontals. Supraoculars flat or convex,
smooth, becoming progressively larger medially such
that medial scales are two to four times larger than
lateral ones. Circumorbitals present, not well dif-
ferentiated from supraoculars. Superciliaries eight
to 13, extremely elongate medial scale occasionally
present. Palpebrals ovoid, slightly convex, inter-